When using the Negative Tester as Master Receiver, how can I get the data received from the I2C slave?

The Negative Tester works like a pattern generator. You can create all kinds of valid and invalid I2C messages. To read back the data from the I2C bus, you need a Tracii XL 2.0 in parallel on the I2C bus. This Tracii XL 2.0 is used as I2C tracer, which captures the data transmitted on the I2C.

Can I add my own test cases into the I2C Studio GUI for the Negative Tester?

Typically the users of the Negative Tester are using the GUI for their first tests. Afterwards the customers typically write the own test cases use the I2C APIs. Most users integrate these test cases into their own testing framework, which communicates with the Negative Tester on one side and with the DUT on the other side.